The goal of this NCNPDDG application is to identify an develop drugs that restore p53 function to deficient cancer cells. The function of p53 is lost in a large number of human cancers. The frequency of loss and recent advances in our understanding of p53 function suggest that p53 normally plays a protective role by arresting the growth of damaged cells or triggering their programmed cell death. Thus restoration of p53 function may provide a therapeutic benefit for many forms of cancer. Recent information on the biochemistry and structure of p53 protein suggests ways to evaluate restoration of function. The DNA-binding function and transactivation capacity of the protein can be exploited to evaluate discrete molecular defects that are appropriate targets for drug discovery based on structural and biochemical data. This Laboratory Program intends to exploit such information to design and develop assays that are amenable to high throughput screening and follow-up evaluation of active compounds in cells and animals. The assays that we develop will target defects in p53 function from missense mutations, MDM2 complex formation and loss of cyclin/CDK inhibition. The specific missense mutations that we are targeting are those selected as potential candidates for reactivation (based on both biochemical data and structural information from Laboratory Program 3). Assays targeting the MDM2 oncoprotein are based on knowledge of the MDM2-p53 interaction and also exploit the activity of wild-type p53. Assays directed to cyclin/CDK activity target both the formation and enzymatic activity of that protein complex. Since a number of the targeted molecular defects are unavailable in adequate cellular and animal models an objective of this Laboratory Program is to design, develop and use these systems to complement the primary screening assays in identifying candidate compounds for development. Our studies will attempt to identify the biochemical mechanism by which active compounds act and will provide an important proof of principle for the further development of the identified leads into drug candidates. Based on the structure and activity of the lead compounds, this Laboratory Program and Laboratory Program 1 will cooperate in carrying out the necessary medicinal chemistry to refine leads into compounds with favorable pharmacological profiles.